Many medical diagnoses rely on non-invasive diagnostic tools to provide information, often in the form of images, descriptive of status of internal portions or organs of a patient. These tools include thermal imaging, ultrasonic probes, magnetic resonance imaging techniques, positron emission tomography, computed tomography (CT), single photon emission-computed tomography (SPECT), optical imaging and/or X-ray based techniques. In some minimally invasive instances, imaging aids, such as contrast-enhancing agents, are introduced into the subject or patient to aid in increasing available data content from the non-destructive imaging technique or techniques being employed.
Each of these tools presents advantages in particularized situations, has technological limitations, may require set-up and analysis time, can include risks and also has associated costs. As a result, a cost-benefit analysis that also reflects the degree of urgency with respect to a particular diagnostic trajectory often favors usage of X-ray based measurement techniques.
However, exposure to X-rays can result in some risk to the test subject or patient. For at least this reason, the dosage of X-rays incident on the patient, organ or object being evaluated/imaged, is often carefully chosen and controlled, for example, variables such as current to the X-ray tube, peak voltage applied to the X-ray tube (kVp) and exposure time, and by selecting and defining an area to be exposed to provide successful imaging, based on the task and the test subject or patient's parameters, with least health risk to the patient or radiation exposure to the object being imaged. The Food and Drug Administration has recently identified X-rays as potentially having carcinogenic effects, adding impetus to the desire to reduce overall exposure while still providing imaging characteristics capable of enabling rapid, effective and accurate diagnostic aids.
Several factors influence image quality resulting from an X-ray procedure. Statistical photon noise resulting from characteristics of the X-ray source and the X-ray generation conditions tends to dominate other noise sources in formation of an X-ray image. Contrast between various image portions, and contrast enhancement techniques, are also important considerations in providing diagnostic images, and these issues require increasingly sophisticated treatment as dose is decreased.
One of the key tenets of medical X-ray imaging is that image quality should be carefully considered in determining exposure conditions, such as predetermined dose considerations delivered to the test subject or patient. The design and operation of a detector used for medical X-ray imaging should therefore be tailored, responsive to the particularized task and measurement conditions, including variables in test subject mass, opacity and the like, to provide high image quality for each X-ray exposure that is incident at its input. One very useful objective metric of quality for electronically-represented images, per input exposure, is detective quantum efficiency (DQE), which represents efficiency of transfer of signal-to-noise ratio from the input signal (i.e., the exposure employed) to detector output.
Pixelated X-ray detectors (detectors comprising a geometric array of multiple detector elements, where each detector element may be individually representative of at least a portion of a picture element in the resultant image) are increasingly being used, particularly for medical imaging. The resulting electrical signals from pixelated detectors may be “read out” individually. Examples of such usage include full resolution (one by one binning), full field of view imaging, in which each detector element in an array individually represents a pixel, and region of interest imaging, in which a subset of the total ensemble of detector elements may each correspond to a pixel, but not all detector elements are employed.
Detector arrays may also be employed in modes in which the signals from more than one individual detector element are combined, prior to electrical conditioning of the resulting electrical signals. Such combination is commonly called “binning” of individual detector signals. In turn, digital or electronic detectors of X-rays and subsequent signal processing of the signals from such detectors increase flexibility in application and thus help to promote reduction of dose of the illumination being employed for non-destructive imaging, which is a desirable goal. The problems addressed by this disclosure involve successfully employing these capabilities to improve performance of a detector array for a particular imaging task.
For the reasons stated above, and for other reasons discussed below, which will become apparent to those skilled in the art upon reading and understanding the present disclosure, there are needs in the art to provide test data in support of reliable diagnoses of medical conditions and diseases from medical anatomical images, providing contrast equal to or exceeding that of conventional approaches, yet using reduced exposure parameters when feasible, consistent with the imaging task.